1. Field of the Invention
The present invention relates to a developing device used in a electrophotographic recording apparatus, particularly to a toner residual amount detecting mechanism of the device.
2. Description of the Related Art
Conventionally some developing devices used in the electrophotographic apparatus are provided with a toner residual detecting mechanism, which rotates a supported stirring shaft extending in the longitudinal direction of a hopper which stores toner supplied thereto, transmits the resistance of the residual toner to the rotor provided on the stirring shaft, and detects the operation of the rotor by a photosensor. For example, such a typical developing device is disclosed in a maintenance manual entitled "Laser Line.TM. 6 elite" pp 3-21 to 22, published by Oki Electric Industry Co., Ltd. in January 1988. This developing device will be described hereinafter with reference to the drawings.
FIG. 2 is a cross-sectional view of a toner residual amount detecting mechanism of the developing device.
The developing device 1 comprises a hopper portion 3 for storing toner 2 supplied thereto, a developing roller 5, a supply roller 6, and a stirring shaft 7 which extend in the longitudinal direction of the portion 3 and is rotatably supported by both side portions of a frame 4, and a blade portion 8 which extends along the surface of the developing roller 5 in the axial direction thereof. The developing roller 5, the supply roller 6 and the stirring shaft 7 each have one end extending out of one side portion of the frame 4 and being connected to a gear. Each of the gears meshes an intermittent gear, not shown, to thereby form a chain of gears. As illustrated in FIG. 3A, the gear 11 coupled to the stirring shaft 7 has a stepped portion 11a and contacts a rotor 12 which rotates together with the gear 11. The stepped portion 11a and the rotor 12 have substantially the same radius. The stirring shaft 7 is fixed to the rotor 12 at one end thereof and the gear 11 is rotatable relative to the stirring shaft 7. The gear 11 and the rotor 12 can be rotatable relative to each other by engaging a stopper 15 provided on the gear 11 into a long slit 14 provided in the rotor 12 and engaging a protrusion 16 provided on the rotor 12 into a long slit 13 provided in the gear 11 wherein the long slits 13 and 14 are arc-shaped relative to the centers of the gear 11 and the rotor 12. An extension spring 18 stretches across a protrusion 17 provided on the gear 11 and the protrusion 16 provided on the rotor 12 so that the stopper 15 of the gear 11 is brought into contact with one end of the long slit 14. At this state, the concave portion 19 provided on the gear 11 is positioned to overlap the concave portion 20 provided on the rotor 12. The developing roller 5 contacts a photoconductor drum 22 as illustrated in a two dot chain line in FIG. 2. The stirring shaft 7 has a stirring device 21 for the toner 2 in the hopper portion 3 for preventing the toner 2 from lumping in the hopper portion 3.
FIGS. 3A and 4A show the state where the toner 2 is stored in the hopper portion 3 while FIGS. 3B and 4B show the state where the toner 2 is not stored in the hopper portion 3.
A sensor lever 23 has a fulcrum 24 at one end thereof, an extension spring 25 provided at the other end thereof and a convex portion 23a provided at the substantially central portion thereof. The convex portion 23 of the sensor lever 23a of contacts the stepped portion 11a and the outer periphery of the rotor 12 by resiliency of the extension spring 25. A protrusion 23b of the sensor lever 23 is retained by a microswitch 26 provided in the developing device.
An operation of the developing device will be described hereinafter.
Since the gear of the developing roller 5 meshes a gear, not shown, for driving the photoconductor drum 22, the developing roller 5, the supply roller 6 and the stirring shaft 7 are rotated in the directions of the arrows B, B and D respectively when the photoconductor drum 22 rotates in the direction of the arrow C as shown in FIG. 2. The toner 2 charged with electricity on the surface of the developing roller 5 is uniformly layered and attached thereon by the blade 8. The toner 2 adheres to an electrostatic latent image formed on the photoconductor drum 22 which rotates at constant speed in the direction of the arrow C and visualizes the electrostatic latent image. At this time, the stirring device 21 rotates together with the stirring shaft 7 in the direction of the arrow D so that the toner 2 is conveyed to the supply roller 6 and it stirs the toner 2 for preventing the toner 2 from lumping therein.
When the residual amount of the toner 2 is sufficiently large in the hopper portion 3, the resistance of the toner 2 applied to the stirring device 21 is high so that the extension spring 18 stretches as illustrated in FIG. 4A in which the rotary force of the gear 11 is transmitted to the rotor 12 to thereby rotate the stirring shaft 7 in the direction of the arrow D while the other end of the long slit 14 of the rotor 12 is in contact with the stopper 15 of the gear 11. At this time, since the concave portion 20 of the gear 11 does not overlap the concave portion 19 of the rotor 12, the sensor lever 23 does not turn so that the microswitch 26 attached to the developing device does not operate. When the residual amount of the toner 2 stored in the hopper portion 3 is small, the resistance of the toner 2 acting on the stirring device 21 becomes weak. The extension spring 18 contracts and transmits the rotary force of the gear 11 to the rotor 12 while one end of the long slit 14 of the rotor 12 is in contact with the stopper 15 of the gear 11 as illustrated in FIG. 4B. As a result, the stirring shaft 7 is rotated in the direction of the arrow D. At this time, the concave portion 20 of the gear 11 overlaps the concave portion 19 of the rotor 12 so that the sensor lever 23 turns when the convex portion 23a of the same enters the concave portions 19 and 20 whereby the protrusion 23b of the sensor lever 23 operates the microswitch 26. In the series of the operations, the residual amount of the toner 2 in the hopper portion 3 is detected.
However, there is the following drawback in the conventional toner residual amount detecting mechanism. When the resistance of the toner to the stirring device is sufficiently high, the extension spring stretches to thereby cause the stopper provided on the gear to be brought into contact with the other end of the long slit provided in the rotor whereby the microswitch does not operate. On the contrary, when the resistance of the toner to the stirring device is low, there occurs an unstable situation where the extension spring contracts so that the stopper provided on the gear is brought into contact with neither one end nor the other end of the long slit provided in the rotor. Resistance received from the toner is varied in proportion to the depth to which the stirring device enters the toner, the stopper vibrates in the long slit in such a situation. At this time, the concave portions of both the gear and the rotor overlap each other to thereby operate the sensor lever.